The invention relates to an improved process for recovering methanol from mixtures containing methanol and water, which process requires less energy for separation.
Propylene oxide may be produced by reacting propylene with hydrogen peroxide in the presence of a titanium-containing zeolite catalyst. Methanol is advantageously used as solvent in this process. When working up the reaction mixture resulting from this process, a mixture is obtained which contains methanol and water. Methanol has to be recovered from this mixture, in order to be able to return it to the epoxidation reaction and to be able to operate the process economically. The water arising from hydrogen peroxide and any water introduced into the process with aqueous hydrogen peroxide, has to be removed from the process. The recovery of methanol from the mixture containing methanol and water consumes a large proportion of the thermal energy expended on the process. To perform the process economically, there is therefore a need for an improved process for recovering methanol from a mixture containing methanol and water, wherein the method exhibits a reduced energy requirement.
WO 02/02544 describes a process for the production of propylene oxide, in which working up of the reaction mixture results in a mixture which contains methanol, water and small quantities of hydrogen peroxide. The document describes separating off water from this mixture by distillation performed in two columns, wherein the pressures are so selected that the bottom of the column operated at low pressure is heated using the vapors from the second column, which is operated at high pressure. The coupling of the columns described in WO 02/02544 makes it possible to reduce the energy requirement for recovering methanol from the mixture.
However, the need still remains for processes for recovering methanol which require less energy than the prior art. This object is achieved by the process according to the invention.